Triglyceride breakdown has been assessed by glycerol turnover and found to be increased in human injury and sepsis, beyond that predicted from plasma glycerol levels. Current studies are examining the turnover of free fatty acids in these patients. Studies are planned to determine whether increasing levels of total parenteral nutrition (TPN) can return these values to normal in acute surgical patients. The administration of TPN at 50% above measured energy expenditure with all non-protein calories as glucose will produce a prompt rise in respiratory quotient to over 1.0 consistent with lipogenesis - in the chronically depleted patient. But this fails to occur in the hypermetabolic phase of acute injury or infection despite the "extra carbohydrate". Current studies are seeking the mechanism for this difference. The percutaneous needle biopsy of thigh muscle in acutely injured patients reveals prompt elevations of certain free amino acids yet a 50% drop in glutamine; changes which are poorly reflected in plasma amino acids. Studies are underway to find whether TPN can selectively prevent or reverse any of these changes. The role of inactivity on the above changes is being studied with normal subjects on total bedrest with controlled intake for comparable periods.